Drug release from layer-by-layer microcapsules: a computational study

Drug releasing microcapsules and nanocontainers are largely used in biomedical applications. Typically, such vehicles consist of a drug-loaded core surrounded by a polymeric shell. Diffusion is by far the dominant mechanism in drug delivery, beside other physico-chemical factors, such as drug dissolution, drug binding, polymer swelling and degradation. We upgrade existing mechanistic models by extending their applications to the composite structures, and characterize the kinetics of the drug transferred from the vehicle into the external targeted medium. We develop a theoretical and computational study aimed at modelling the drug release from a composite spherical core-shell capsule having either a protective coating, under the assumption of radial symmetry. The problem of release from such a layer-by-layer composite systems is described by a system of coupled partial differential equations, which we solve with a finite difference discretization and Runge-Kutta type method. In-vitro drug release experiments under different conditions are used to identify the relevant model parameters by an optimization strategy. Drug release profiles are given to show the dependence and sensitivity to parameters, such as diffusivity, dissolution, solubility and binding rate coefficients and the responsiveness to of environment factors, such as pH. The release curve characterizes the drug transport mechanism and suggests how to guarantee a controlled release. The proposed model constitutes a simple tool to predict the release from composite materials that, measuring their performance or comparing different configurations, can help in designing novel drug delivery systems.